This project has as its main objective the improvement of methods for evaluating materials used in surgery. It is an extension of a previous project in which (1) methods of assay of tissue reaction to implanted materials were devised; (2) the relative tolerance of tissues to different metals was portrayed; (3) the in-service performance of metal implants was studied, with particular reference to failure in performance due to intolerance of the tissue to the metal or corrosion products. The extension of the project has as its primary goal a better assay method, to allow better pretesting of new alloys (and perhaps other nonmetallic materials such as polymers, ceramics, composites), and as subsidiary objectives, to refine failure-evaluation data, and to collaborate with the M.I.T. facilities in developing better alloys and better testing methods for them.